The most widely used lubricating greases are calcium base grease, lithium based grease, calcium-sodium based grease and molybdenum disulfide grease, etc. The same consistency prevents an optimal lubrication performance. The reduction factor ranges must be selected from a range. The designation of lubricant grease is indicated by the grade of needle penetration. Most machines use a lubricant that is selected to match the most severe demand of one component in the machine such as a bearing, gear, etc.
It is the stated policy of American Roller Bearing Company that we do not recommend a specific lubricant or even a company that manufactures lubricants. For the widely used lubricant grease, we judge the grease whether it loses its efficacy or not by examining the function parameter of the grease. The motion of the bearing distributes the oil as it rotates through an oil bath located at the base of the bearing. The roller tilt angle increases with the increase of the plastic viscosity. The results demonstrate that these lubricating greases have good friction-reducing function under fretting and sliding conditions, and their friction reduction is superior to wear resistance, especially calcium sulfonate complex grease. The system uses a pump to circulate oil through the bearing. Ten deep-groove ball bearings are fitted into five housings and filled with a given quantity of grease.
Grease has self-healing properties where fresh grease is supplied in case of film breakdown and self-induced heat development. In applications such as this, it is often beneficial to completely wash out the bearings once a year, re-pack with new grease, and continue on with the established re-greasing program. To accelerate such a test, the outer ring of the test bearing is heated, which accelerates the aging process and reduces the viscosity of the grease. Grease lubrication is widely applied to rolling bearings. Sealed bearings have been filled with grease before leaving factory and can be applied directly in service. The actual lubricant for a rolling bearing is oil, which can be a mineral oil, fully synthetic or a blend of the two. The most important property of any lubricant for rolling element bearings is its oil viscosity.
Grease-lubricated Bearings in Electric Motors A greased roller bearing in an electric motor is offered to demonstrate the possible grease service life. Grease lubricant has a high adaptability to great changes of load chrematistics and moving speeds, so it can be used in those machineries whose working ambient temperature and speeds change greatly. The viscosity of lubricating grease is so high at very low shear rates that only creep flow will occur, and the grease has an apparently solid behavior. Generally, greases with light consistency can be used at low temperatures. The depth of penetration is measured on a scale of 1 to 10 mm.
If possible, relubrication should be carried out during operation. There is no consensus on the next phase in the lubrication process. It is important to remember that re-lubrication should be done when grease in the bearing is still good. Bearings not sealed for life or factory-filled should be filled with grease with sufficient free space in the housing up to 50 percent to allow room for the excess grease to be ejected from the bearing during startup. This may occur a number of times, depending on the healing ability of the grease, which is a function of the ability of the grease to maintain its fluidity. At the end of the test cycle, the degree of corrosion is evaluated according to a scale between zero no corrosion and five severe corrosion. The authors present a model that can be used to predict the decrease of oil-layer thickness due to centrifugal forces as a function of position across the track for different types of bearings.
It is important to select the right grease for specific requirements and to calculate the lubricant life cycle. Grease-lubricated bearings have sufficient operational reliability if the relubrication intervals are not exceeded. Dry compressed air and oil mixture are transported to every part of bearing where it needs lubrication. Some machine designs provided a purging vent or allow the old grease to escape under seal lips. The selection of any lubricant over another should always consider additives.
This avoids damage to bearings, extends the durability of the bearing and increases operational reliability. Relubrication is necessary when the grease operating life is lower than the expected bearing operating life. Regulated flow is easily adjusted for optimum performance. In applications where bearings are operating at very low speeds and require good contamination and corrosion resistance, it is recommended that the housing be completely filled with grease. An Alassca complex grease will meet and surpass the requirements for this kind of product without the use of conventional 'additives'. If relubrication has not taken place, severe film breakdown will result, called the end of grease life, which subsequently leads to bearing damage and failure. The test is conducted at a predetermined speed and temperature.
This so called equipartition assumption has been verified experimentally, measuring the lubricant layer thickness after separation of an oil layer between a plate and a cylinder. In the latter case, the film thickness will increase again, resulting in sufficient lubrication until the next event takes place. Machine oil and engine oil are suitable as base oil for mid-speed bearings. In reality, bearing failures still occur after 15,000 to 20,000 hours with this type of bearing. Each of these has its own features, so the lubrication method that best offers the required function must be selected. Grease cleanliness is as important as the proper amount. Upon rotation the grease is distributed within the bearing, however, only the bearing should be completely filled with grease prior to start-up and the free space in the housing should only be partially filled.
Consequently, it is possible to determine grease life factors based on performance within a range of temperatures. Further tasks fulfilled by the lubricant in the rolling bearing are, depending on the type of lubricant oil or grease with corresponding additives , corrosion protection, extraction of heat from the bearing, protection of the bearing against inner and outer soiling, damping of the bearing running noise, as well as support in the sealing effect of bearing seals. Grease is the most common type of lubricant used for rolling bearing lubrication today. Today it is possible to predict to a good extent the lubricating life of grease and to monitor its remaining life. Fretting behaviors depend on not only grease-film and chemical reaction film, but also fretting wear mechanisms including abrasion, oxidation, and delamination. Such centrifugal effects play a role in e. The lubrication system should be designed to handle a grease that is best suited for the bearing.
A set of high-quality, high-sensitivity bearings are lubricated with the candidate grease and placed in housings in the test stand. Gellant type is also found to be important. These represented a huge improvement in drive technology, increasing the switching frequency to 20 kHz, reducing harmonics and audible noise. It describes greases and the advantages they have over oil. The final chapter covers lubrications systems — the systems that deliver grease to the components requiring lubrication. Nozzles inject oil directly into the bearing providing a duel function of lubrication and removal of heat.